1. Field of the Invention
The present invention relates to thixotropic isocyanate-terminated prepolymers. More particularly, the invention relates to prepolymers prepared from certain graft polyols containing unsaturation and certain organic polyisocyanates.
2. Prior Art
The preparation of isocyanate-terminated prepolymers from organic polyisocyanates and polyols is well known in the art. In addition, U.S. Pat. No. Re. 29,014 teaches that graft polyols containing unsaturation can be reacted with organic polyisocyanates to obtain prepolymers for use in the preparation of polyurethane compositions. This patent does not teach the reaction of any specific graft polyol with any specific organic polyisocyanate to prepare an isocyanate-terminated prepolymer.
The use of isocyanate-terminated prepolymers in the preparation of urethane coating compositions is also well known in the art. Normally, however, thixotropic agents must be added to the compositions to achieve nondripping characteristics. The present invention is based on the finding that a select group of reactants results in prepolymer compositions which are thixotropic and thus find special utility in the preparation of polyurethane coating compositions.